Exhaust systems for high-performance internal combustion engines of the type used on racing cars have been the subject of considerable empirical design work and some theoretical studies. However, exhaust systems are often treated secondarily by racing teams and car manufacturers in the effort to increase engine performance. They generally are regarded as necessary evils which only contribute insignificantly to increase, and more conventionally are thought to decrease, engine horsepower.
Header exhausts form one portion of an exhaust assembly which are typically known to produce gains in horsepower. Because high performance engines are generally designed to rev at high speeds, a freer flowing exhaust is highly beneficial. Thus, headers improve exhaust flow while, further, beneficially reducing engine operating temperature.
Mufflers, on the other hand, with their internal baffling, ordinarily impede exhaust flow which increases back pressure. Typically, mufflers include sound attenuating partition configurations that baffle sound or disperse gas within the muffler. Some designs produce low pressure regions or volumes which can be the result of cancellation of identical sound frequencies by directing streams of gas to collide against each other, or can be the result of fluid flow patterns through the muffler, or both. However, such collisions of gas may induce back pressure, which generally reduces engine performance, or may increase operating temperature and reduces gas mileage. As such, mufflers are primarily used and developed for the attenuation of the sound component of an exhaust's gases from an internal combustion engine rather than applied to enhance engine performance.
The prior art contains various muffler constructions which purport to solve the problem of sound attenuation without producing the above-mentioned undesirable effects. Realistically, however, racing cars normally run straight pipes, eliminating the muffler.
At low engine speed, typically measured in revolutions per minute or RPM, a slight back pressure may aid acceleration and, thus, be beneficial. However, at a high RPM, back pressure is highly undesirable because it impairs breathing of the motor which limits the top speed. Sometimes, however, even in racing applications, mufflers are required.
As previously mentioned, some muffler designs produce a low pressure volume in the muffler chamber which has been found to be desirable since, in some muffler configurations, increases in horsepower have been measured.
Two mufflers which employ these principles and have been highly effective in sound attenuation while increasing engine horsepower are the muffler of my U.S. Pat. Nos. 4,574,914 and 5,123,502. These mufflers are now in widespread use by independent professional race car drivers and even by some of the manufacturer sponsored racing teams.
Other prior art mufflers which seek to effect sound attenuation while minimizing back pressure include: U.S. Pat. Nos. 624,062; 1,184,431; 1,081,348; 2,071,351; 2,325,905; 2,239,549; 2,485,555; 2,667,940; 2,971,599 and British Patent No. 285,604.
Recently, it has been found that exhaust header assemblies may be constructed that substantially increase horsepower. Such a header assembly is set forth in my pending U.S. patent application Ser. No. 07/566,983.